1. Field of the Invention
The present invention relates to a manufacturing method of a hermetically sealed container. The present invention particularly relates to a manufacturing method of a display panel having a device provided therein which may have lower performance by the ingression of oxygen, water and the like.
2. Description of the Related Art
Image display apparatuses of a flat panel type such as an organic LED display (OLED), a field emission display (FED) and a plasma display panel (PDP) are well-known. These image display apparatuses are provided with an envelope which is manufactured by hermetically bonding glass substrates that oppose each other and has an inner space isolated from an outer space. In order to manufacture these hermetically sealed containers, a space-specifying member and a local adhesive material are arranged between the glass substrates that oppose each other as needed, a bonding material is arranged in the periphery so as to form a frame shape, and the materials are heated to be bonded. As for a method of heating a bonding material, there are known a method of baking the overall glass substrate in a heating furnace and a method of selectively heating the periphery of the bonding material by local heating. The local heating is more advantageous than the overall heating, from the viewpoint of heating and cooling periods of time, energy necessary for heating, productivity, the prevention of thermal deformation of a container, the prevention of thermal degradation of a functional device arranged in the inside of the container and the like. Particularly, a laser light is known as a unit of the local heating. It is also known that the manufacturing method of the hermetically sealed container by using a local heating unit can be applied to a manufacturing method of a vacuum heat-insulating glass which does not have a functional device provided therein.
A manufacturing method of an envelope of an OLED is disclosed in U.S. Patent No. 2006/0084348. Firstly, an assembled structure is prepared that includes a first glass substrate and a second glass substrate which sandwich a bonding material arranged so as to form a perimeter. Next, this assembled structure is scanned by being irradiated with a local heating light, while keeping the state sandwiched with a pair of a transparent silica disks. Thereby, the bonding material in a perimeter is melted, and the first glass substrate and the second glass substrate are hermetically sealed.
A manufacturing method of an envelope of an OLED is disclosed in U.S. Patent No. 2009/0044496. Firstly, a frit glass is formed in a perimeter having a corner portion on the first glass substrate which has been employed as a supporting substrate. The first glass substrate having the frit glass provided thereon and the second glass substrate are opposed to each other to sandwich the frit glass, and are assembled. In the assembly, the first glass substrate and the second glass substrate are pressurized by a mechanical unit from the outside, and the adhesivity in a bonding material region is secured.
Thus, bonding methods are known which do not simply irradiate a glass substrate that is a material to be bonded and a bonding material with a laser light, but have variously improved an assembly method, so as to secure the adhesivity between the bonding material and the glass substrate when having been irradiated with the laser light.
However, there has been the case in which adhesivity between the glass substrate that is the material to be bonded and the bonding material is insufficient in an assembled stage before the bonding is finished, and a bonding failure occurs. The securement of the adhesivity which is a subject of the present invention will be described in detail below.
The above described adhesivity is associated with a relationship between the size of a region to be locally heated and a substantial uneven pitch on the surface of a bonding material in a region scheduled to be bonded. FIGS. 4A to 4F are sectional views illustrating a state of the bonding of a substrate 101 and a frame member 103. FIGS. 4A to 4F illustrate the case in which the bonding material is provided on a substrate 101 side for convenience, but the following description is also applied to the case in which the bonding material is provided on a frame member 103 side. In addition, the following description is also applied to the case in which substrates are bonded to each other, or the case in which a substrate is bonded to a substrate having the frame member provided thereon. FIG. 4A illustrates a contacting state in a pressurizing step in the case in which the uneven pitch on the surface of the bonding material 104 is smaller than a region 107 to be irradiated with a laser light (diameter of laser spot), and FIG. 4B illustrates a contacting state when the bonding material has been irradiated with the laser light in the pressurizing step. Because the bonding material 104 is swollen and deformed by being softened and melted, a leveling action of the bonding material 104 is expected even in a region in which the bonding material 104 is not brought in contact with the frame member 103 in an unheated stage. For this reason, continuous bonding can be obtained in the region which has been irradiated with the laser light.
On the other hand, when the uneven pitch of the surface of the bonding material 104 is larger than that of the region 107 to be irradiated with the laser light, the following problem occurs. FIG. 4C illustrates a contacting state in the pressurizing step, and FIG. 4D illustrates a contacting state when the bonding material has been irradiated with the laser light in the pressurizing step. Because the uneven pitch of the surface of the bonding material 104 is large, even when the bonding material 104 is swollen and deformed by being softened and melted, a sufficient leveling action does not occur in the bonding material 104. Because of this, a bonding failure 105 partially occurs in a bonded portion. Generally, when the uneven pitches of the surfaces of the substrate and the frame member are sufficiently larger than the plate thicknesses of the substrate and the frame member, the substrate and the frame member are wholly pressed through an unshown cover plate, accordingly the substrate, the frame member and the cover plate are warped, and the overall adhesivity is easily secured. However, even in that case, an uneven pattern of a long pitch locally remains on the surface of the bonding material, and accordingly the adhesion failure occasionally occurs. In the case of overall heating, the bonding material also is wholly heated, accordingly a leveling action occurs simultaneously in a wide range, and such a problem resists occurring comparatively. In contrast to this, in the case of local heating, the bonding material is not softened and melted in a place other than the region to be locally heated, and accordingly a range in which the leveling action occurs is limited. Because of this, a partial bonding failure tends to easily occur.
There is also the case in which particles inevitably get mixed in a region scheduled to be bonded. FIG. 4E illustrates a contacting state in a pressurizing step, and FIG. 4F illustrates a contacting state when the bonding material has been irradiated with a laser light in the pressurizing step. The bonding material 104 is swollen and deformed along with being softened and melted, but the degree of deformation is not sufficient to cause the leveling action in the periphery of the particles 106, and accordingly the bonding failure 107 partially occurs in the bonded portion.
There is the case in which the partial bonding failure occurs also by the thermal expansion and thermal shrinkage of the substrate and the frame member in a portion to be locally heated. This is also a phenomenon peculiar to the local heating.
As described above, when materials are hermetically bonded with the local heating unit, it is extremely important to reduce a noncontact region in an unheated stage as much as possible, though perfect adhesivity such as in an optical contact is not needed.
Pressurization by a mechanical pressing unit as is disclosed in U.S. patent No. 2009/0044496 is indirect pressurization through a firm structure, the pressing force resists being uniformly applied to the materials, and accordingly there has been the case in which the pressurization is not necessarily sufficient for suppressing the adhesion failure. For this reason, a method has been desired which locally heats the region in a state of resisting being affected by the uneven pattern of a long pitch on the surface of the bonding material and the mixing particle, and making an adhesive force more uniformly applied to the materials.
An object of the present invention is to provide a manufacturing method of a hermetically sealed container, which improves adhesivity in a region to be bonded and thereby enhances the reliability, when sealing a container to be hermetically sealed by the scan of the locally heating unit.